Change display of item name on mobile/narrow windows

[poliorcetics]

First discussed in #79936.

After #79936, rustdoc will display items names as such:

I wonder if something like this would be better in term of usability. It would add more scrolling but narrow screen, especially mobile ones, are made for scrolling:

(This is a dirty photo-montage, sorry for the low quality)

@rustbot label T-rustdoc A-rustdoc-ui

[jyn514]

Duplicate of #78799